Wave generator



May 25, 1954 K, N, FROMM 2,679,594

WAVE GENERATOR Filed Feb. 28, 1950 lNvENToR KennethNFromm.

ATTORN EY WlTN ESSES:

aww

fsome Vof the functions of a vacuum tube.

Patented May 25, 1954 WAVE GENERATOR Kenneth N. Fromm, Pittsburgh, Pa.,assgnor fto Westinghouse Electric Corporation, East Pittsburgh, Pa., acorporation of Pennsylvania Application February 28, 1950,Serial"fNo.1146,715

( Cl. Z50-36) 3 Claims.

My invention relates to electronic circuits, and

more particularly to electronic circuits of the type designed togenerate various Wave forms.

Wave-form generators in accordance With the .prior art of which I amlaware include electric discharge devices and their associatedcomponents such as cathode transformers. These generators are relativelycomplicated and bulky and their components are costly.

It is accordingly an object of my linvention to provide la Wavegenerator vwhich is simpler and less costly than prior art apparatus forperforming a similar function.

It is another object of lmy invention to provide Aa Wave generator whichshall require a minimum of circuit components.

It is an object of my invention to -provide a pulse generator which isversatile in its Aoperation.

Recent developments'in the artof'solidfconduction have produced a devicewhich can perform This rdevice termed a transistor -comprises va blockof semi-conductive material, such as silicone 01' germanium, with whichare associated vthreee'lectrodes. Two of these electrodes, called the`emit-- ter and the collector, `are conductive probes Ahaving relativelysmall contactareas, andare located near eachother on 'one fface of thesemi-conductive lblock. rilhe third electrode, called Va vbaseelectrode, which isa conductor having a relatively large contact area,is 'placed Icontiguous Ato fthe opposite face ofthesemi-conductiveblock.

In Vaccordance with my invention, I provide a lWave rgenerator .circuitutilizing a transistor. A Wave generator yconstructed in accordance withmy invention is versatile in operation and is simple .and compactinvstructure.

lMy :invention together with additional Jobjects yand radvantagesthereof, will be `best understood :from .the :following descriptionltaken in iconnec- :tion with the accompanying drawing, lin which:

Figure l is a schematic diagram showing-apre- 'ferred embodiment of myinvention,

Fig. 2 is a schematic diagram showing'a modication of the embodimentofFig. '1,

Fig. 3 is a schematic diagram of another vembodiment of my invention,and

Fig. '4 is a'schematic diagram showing a yfurther embodiment of myinvention.

In Fig. 1 there is shown a semi-conductive device vwhich `may 'be atransistor, indicated gen- `'erally at II. The transistor I'I-comprisesablock .of semi-conductive material I3 which may -be-siliconeor germanium YandWith-whicharcassociated emitter, collector and baseelectrodes I5, I 1 and I9, respectively. The emitter and collectorelectrodes I5, I1 are pin-pointed conductive :probes which are locatedin proximity to each other on one face of the semi-conductive block I3.The base electrode `I9 isa plate of conductive material which is `placedcontiguous lto the ropposite face yof the semi-conductiveblock. Positivebias is supplied to the emitter electrode I5 :from a direct-current biaspotential source `indicated generally at 25. This bias potential source25 may take any convenient form, but is .preferably variable, and isshown asa battery 3l connected in shunt vwith a potentiometer l33. Theemitter electrode |15 is connected vthrough a first lresistance 2| tothe adjustable tap 23 of the potentiometer .33. The junction of thepotentiometer 33 Aand the negative terminal 21 of the battery 3| isconnected to ground at '29. The lcollector electrode Il is connectedthroughxa second resistance 35 to the negative terminal '31 of adirect-current bias potential source which is shown as a battery 39, thepositive terminal 4I of which is connected to ground at '29. Thenegative terminal 31 ,of said last mentioned bias rpotential source isconnected through a by-pass capacitance 43 to ground at 45. The baseelectrode I9 is connected through a variable resistance 41 to ground at2'9.

The `circuit just described may be used to produce either continuous orkeyed pulses of any desired Width or repetition frequency within thefundamental transit -time limitations of the vtransistor II. Thevariable resistor 41 provides a positive feedback loop which causesoscillation when the feedback assumes a magnitudeof suiiicient value tobe sustained. An increase `of the magnitude of the variable resistance41 beyond this critical magnitude will result in an increase in therepetition frequency. The pulse `Irisetime is thought to be primarily aninnate property-of `the .semi-conductive material of the transistor. Thedecay time is lthought to be primarily a function of the collectorresistance Aand capacitance as well as the emitter collectorcapacitance. If it is desired to key the generator, the emitter bias isadjusted to a magnitude which `blocks oscillation. Application of akeying pulse `through a suitable coupling means, shown in Fig. 1 as acapacitor 43, yto the emitter Ythen allows oscillation for the timeduration of the :keying pulse. It is thus possible to produce groups ofpulses at a selected repetitionrate. Pulse .repe-f tition rates as highas 56,0 lkilocycles .arereadily obtainable and higher rates' karepossible with reduced distributed capacitance. `Pulses with a 'theemitter capacitance.

tion, a second variable resistance 49 in shunt with a capacitance isinserted between the rst variable resistance 41 and the transistor baseelectrode I3. The battery potential source is eliminated and the emitterelectrode I5 is connected through the rst resistance 2| to ground at 29.In practice, the magnitudes of 2000 ohms and 0.1 microfarad respectivelyhas been used for the last mentioned resistance and capacitance.

Fig. 3 shows an embodiment of my invention in which the repetitionfrequency of the generated pulse is determined primarily by a resistancecapacitance combination in the emitter circuit. In Fig. 3, the emitterelectrode I5 of the transistor is connected through a rst resistance 2|in shunt with a capacitance 53 to ground at 29. The collector electrodeI1 is connected through a second resistance 35 to the negative terminal31 of a direct-current bias potential source shown as a battery 39, thepositiveterminal 4| of which is connected to ground at 29. The baseelectrode I9 is connected through a third resistance B5 to ground at 29.The circuit shown in Fig. 3 produces pulses having very sharp leadingedges, the rise times of which are dependent upon the magnitude of At arepetition frequency of 500 kilocycles using a 50 micro-microfarademitter capacitance, the rise time is of the order of .5 micro-second.The repetition may be varied by changing the magnitude of either theemitter bias resistance 2| or the emitter capacitance 53. In operationof the circuit of Fig. 3, the following circuit constants have been usedand parameters noted: Emitter capacitance,

l microfarad; emitter resistance, 10 megohms; l

A wave form. In this embodiment, a single transistor II is utilized toproduce a saw tooth wave form, whereas two or more vacuum tubes arecommonly used in such generators of the prior art. In Fig. 4, theemitter electrode I5 is connected through a first resistance 2| to thepositive terminal of a direct-current bias potential source shown as abattery 3|, the negative terminal 32 of which is connected to ground at29. The collector electrode I1 is connected through a second resistance35 to the negative terminal 31 of a direct-current bias potential sourceshown as a battery 39, the positive terminal 4I of which is connected toground at 29, The base electrode I9 is connected to a. variableresistance 51 to ground at 29. A capacitance 59 is 4 connected betweenthe emitter and collector electrodes I5, I1.

In practice, the variable resistance 51 is adjusted to a magnitude whichwill provide suflicient feedback for oscillation with an appropriateemitter bias voltage. rThe frequency of oscillation may be varied bychanging the magnitude of the capacitor 59 which is connected betweenthe emitter and collector electrodes I5, I1. The magnitude of said lastmentioned capacitor 59 may be chosen so as to get a pulse rise time assmall as 116 microsecond. If a triggered or synchronized wave isdesired, it may be obtained by adjusting the emitter bias so that thecircuit is no longer free running and applying synchronizing pulsesthrough a suitable coupling means shown in Fig. 4 as a capacitance 48 tothe emitter electrode I5. By means of a differentiating circuit, verysharp pulses may be obtained due to the inherent small raise time of thewave form. Proper adjustment of the variable resistance 51 and theemitter-collector capacitance 59 in combination will provide improvedlinearity,

The circuit of Fig. 4 has been found to operate well using the followingcircuit constants: Emitter bias resistance, 470 ohms; collector biasresistance, 30,000 ohms; base electrode variable resistance, 1,400 ohms;emitter collector capacitance, 0.007 microfarad. With these constantsthe repetition frequency was 3 kilocycles, the collector current 2.4milliamperes and the emitter current 1.5 milliamperes.

While I have shown certain specific embodiments of my invention, I amaware that certain modications could be made without departing from thescope of my invention. I desire, therefore, to be limited only insofaras is necessitated by the prior art and the spirit of the appendedclaims.

I claim as my invention:

1. A circuit for generating a saw tooth wave form including a device ofthe semi-conductive type having emitter, collector, and base electrodes,a first resistance connected from said emitter electrode to the positiveterminal of a rst direct-current potential source, the negative terminalof which is connected to ground, a second resistor connected from saidcollector electrode to the negative terminal of a second directcurrentpotential source, the positive electrode of which is connected toground, a feedback resistance connected between said base electrode andground, and a capacitance connected between said emitter and collectorelectrodes.

2. A circuit for generating a saw tooth wave form including a device ofthe semi-conductive type having emitter, collector, and base electrodes,a rst resistance connected from said emitter electrode to the positiveterminal of a rst direct-current potential source, the negative terminalof which is connected to ground, a second resistor connected from saidcollector electrode to the negative terminal of a second directcurrentpotential source, the positive electrode of which is connected toground, a variable feedback resistance connected between said baseelectrode and ground, a capacitance connected between said emitter andcollector electrodes, and means for coupling a source of synchronizingsignals to said emitter electrode.

3. A pulse generator comprising a transistor having emitter, collector,and base electrodes, an external network interconnecting saidelectrodes, said network including a rst path extending from thecollector electrode to the emit- 5 6 ter electrode by Way of whichcollector output References Cited in the file of this patent power iSfed back t0 emitter, and a Second path common to the emitter andcollector electrode circuits by way of which collector output NumberName Date power is fed back to the emitter, said first path 2,517,960Barney et a1 Aug 3 1950 comprising a, capacitor connected between said2,556,286 Meacham June 12 1951 collector and emitter electrodes, andsaid second OTHER REFERENCES path comprlslng a feedback resistorconnected Rh C' A. Review, March 1949, pages 5 16 M between said baseelectrode and a terminal which ticle entitled Some Novel Circuits forthe Three rlrntnon to the emlttei and collector electrode 10 TerminalSemiconductor Amp1ier

